The utility and enjoyment of computer systems can be enhanced by providing better user interfaces. User interfaces for computers systems have evolved significantly since the personal computer (PC) first became widely available. Early PCs were limited to user input devices, such as the keyboard and serial mouse, and were primarily text-based. However, a vast improvement in the speed and the power of microprocessors, a much greater available low-cost memory, and improved programming functionality have all contributed to the advancement of much more sophisticated user interface designs and the development of user-friendly graphic operating systems and hardware.
One particular area of advancement in user interface technology pertains to the recent development of an interactive display, to which a number of commonly assigned patent applications have been directed. An interactive display presents graphic images to a user on a flat surface, such as the top of a table or other housing format. In addition, this surface is responsive to input by a user. A PC is coupled to the interactive display to provide the processing power that yields a rich user interactive experience, offering more sophisticated command and interface features, and a far more natural interactive approach in providing input to the system, particularly as related to displayed images.
Interactive display systems that have been developed typically employ an optical system for generating images, and for detecting user input. However, such optical systems usually require an image projection system, which is relatively expensive, requires a relatively large housing, and which must be maintained in close alignment relative to the optical components that sense input. One alternative developed to address the inherent problems of a projection system for image display is the use of a liquid crystal display (LCD) panel. LCD displays work by changing the polarization of incident light and by filtering out light which is not polarized in the same orientation as the LCD. This function is typically achieved using a sandwich of fixed polarizing sheets and active liquid crystal elements. The activation of the liquid crystal elements controls the amount of light that is able to pass through each part of the display. Additionally, a mosaic of color filters is overlaid or embedded within the LCD panel so that individual elements only transmit specific ranges of visible light, thus achieving a full color display. However, an interactive display must also be configured to detect objects placed on or near the surface upon which images are displayed. For example, a camera can be placed behind the surface to sense light reflected from an object on or immediately adjacent to the surface. Unfortunately, using visible light illumination for object detection would interfere with an image displayed on the LCD panel.
A typical illumination source for an LCD panel is a thin fluorescent tube that produces light input to the edge of a sheet of transparent material, such as acrylic, that comprises the panel. Light from the fluorescent tube travels within this acrylic sheet light guide, bouncing off the surfaces due to internal reflection until it reaches a point on the surface which has been deliberately roughened, enabling the light to escape the light guide. Other light guide techniques include the use of scattering of bumps or an angled wedge. However, many LCD panels are quite translucent and if the illumination of the LCD panel is not uniform within the enclosure that houses the LCD panel, darkened areas can appear when the display is viewed at certain angles.
Therefore, there is current interest in finding solutions to the above problems with LCD panels for use with an interactive display that can provide detection of items on a display surface, while also providing uniform surface illumination when viewed by users, regardless of the viewing angle. The solution should enable the display of graphic images on the panel while not interfering with the detection of objects on or near the surface of the panel. Thus, it will be important to avoid using an illumination source for detecting objects that produces light visible to the user, since that would interfere with the displayed image. Of course, it is also important that items on the display surface be detected, regardless of the currently displayed image.